(a) Technical Field
The disclosure relates to a method for semiconductor wafer processing.
(b) Description of the Related Art
In vertical furnaces used for semiconductor wafer processing, a wafer boat may be used for accommodating a stack of vertically spaced apart wafers. Typically, as shown in FIG. 1, a conventional wafer boat 100 comprises two side rods 110A and one back rod 110B which extend vertically between a top member 120 and a bottom member 130. Each rod includes vertically spaced recesses 150 facing inwardly (i.e. generally towards a central axis of the wafer boat 100) along the length of rod. Each recess serves as a support arranged for engaging a circumferential side portion of a wafer, and recesses at a same height define a wafer accommodation for receiving and supporting a wafer in a substantially horizontal orientation. Wafers can be inserted into and removed from the boat at an open side of the boat, opposite of the back rod 110B.
Such wafer boats are used for oxidation diffusion processes but also for chemical vapor deposition processes. When the thickness of a film deposited in a batch furnace exceeds a few microns, the deposited film sticks the wafer onto the rods of the wafer boat. When the wafers are unloaded from the boat by a wafer handling robot, the wafer may remain attached to the boat, resulting in a wafer handling error or the wafer can be unloaded but is damaged during the process of separating the wafer from the boat. Parts of the wafer may break away during the separation process which is undesirable. One solution can be to limit the thickness of the film that is deposited in one run, unload the boat from the furnace and unload the wafers from the boat; then load the wafers into the boat again, load the boat into the furnace and carry out a next deposition process. This can be repeated until a desired cumulative film thickness is achieved. However, this is a time consuming process and not very efficient.